Say no. Explain why. Emphasize that if they continue to use they need to lower their expectations of what pharmacotherapy can do. Secondly, counsel about the serotonergic properties of cannabinoids and potentially increasing risk of serotonin syndrome.
I'd rough estimate 20-33% of my cannabinoid patients continue to follow up after one visit. I had one stick around for several visits, and was consistently not making progress, as expected. The patient recently found another 'provider who is a better fit.' Those who do take the professional advice to quit, or slowly reduce, are making progress.
No to cannabinoids.
I wish cannabis were a panacea cure all treatment. I could quit psych, became a marijuana farmer and have a leg up on the competition because its Dr Recommended. But it's not. I've had some clinic days where 50% of my patients for the day was spent saying 'No cannabis, stop cannabis'.